The aim of this proposal is to identify a spontaneously occurring animal model of bronchial hyperreactivity which physiologically mimics the bronchial hyperreactivity observed in human asthmatics. Equids are the only domestic mammals which spontaneously develop a recurrent bronchial obstruction similar to asthma and affected animals are hyperreactive to intravenous histamine and aerosol antigen administration. This proposal will determine if ponies with recurrent bronchial obstruction provide a suitable model of bronchial hyperreactivity. The objectives of the proposal are: l) to collect two population of ponies, one group with recurrent bronchial obstruction and one normal group. 2) to determine if the pulmonary functional abnormalities of the diseased group are similar to the functional abnormalities of human asthmatics. 3) to determine changes in pulmonary function during disease remission. 4) to compare the dose response of the airways in the two groups to aerosol histamine, methacholine and citric acid. In the diseased group we will determine changes in dose response during acute diseases and during remission. 5) to determine the role of the sympathetic and parasympathetic system in any differences in dose response of the airways observed in the two groups. Dynamic compliance, pulmonary assistance, force oscillatory conductance, functional residual capacity and blood gas tensions will be measured in unanesthetized horses as indicators of large and small airway caliber. To more precisely define peripheral airway abnormalities we will measure density dependence of maximal expiration flows in anesthetized ponies. If the pony provides a suitable model of reactivity, our long term goal is to use the model to investigate the pharmacologic and neurologic control of hyperreactive airways.